Apparatus and method for gas separation

ABSTRACT

Herein disclosed is an apparatus that includes a porous rotor positioned about an axis of rotation and surrounding an interior space wherein the porous rotor comprises sintered metal or ceramic; an outer casing, wherein the outer casing and the porous rotor are separated by an annular space; and a motor configured for rotating the porous rotor about the axis of rotation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/708,862 (now U.S. Pat. No. 8,277,540), filedFeb. 19, 2010, which application claims the benefit under 35 U.S.C.§119(e) of U.S. Provisional Patent Application Ser. No. 61/154,189 filedFeb. 20, 2009. The disclosure of each application is hereby incorporatedherein by reference in entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention generally relates to the separation of gases. Morespecifically, the present invention relates to separation of light andheavy components of a feed gas via centrifugation. Even morespecifically, in embodiments, the present invention relates to gasseparation via centrifugation utilizing a porous rotor.

2. Background of the Invention

Separation of gases, especially gases having similar molecular weights,is a challenging task. Isotope separation is a particularly difficultand energy intensive activity. For example, separating uranium intonaturally-occurring uranium-238 from uranium-235. Around 99.284% ofnaturally-occurring uranium is uranium-238, while about 0.711% isuranium-235, and about 0.0058% is uranium-234. Enriching uranium isdifficult because the two isotopes have very nearly identical chemicalproperties, and are very similar in weight: uranium-235 is only 1.26%lighter than uranium-238. Separation methods, including diffusiontechniques and centrifugation, that exploit the slight differences inatomic weights of isotopes have been employed to separate isotopes ofuranium and produce depleted uranium consisting mainly of the 238isotope, and enriched uranium having a higher-than-natural quantity ofthe uranium-235 isotope.

Diffusion techniques are used to separate similar-molecular weightgases. Gaseous diffusion is a technology used to produce enricheduranium by forcing gaseous uranium hexafluoride through semi-permeablemembranes, typically silver-zinc membranes, and separating the differentisotopes by difference in diffusion rates. This produces a slightseparation between the molecules containing uranium-235 and uranium-238,as uranium-238 is heavier and thus diffuses a bit more slowly thanuranium-235. Thermal diffusion applies the transfer of heat across athin liquid or gas to accomplish isotope separation. The processexploits the fact that the lighter uranium-235 gas molecules willdiffuse toward a hot surface, and heavier uranium-238 gas molecules willdiffuse toward a cold surface.

Centrifugation is also known for the separation of gases of similarmolecular weight. A gas centrifuge is a separating machine specificallydeveloped to separate uranium-235 from uranium-238 by applying forces tothe gas mixture by placing material inside a mechanism that rotates thematerial at high speed. The gas centrifugation process uses a largenumber of rotating cylinders in series and parallel formations. Therotation of each cylinder creates a strong reactive centrifugal forceaccelerating molecules based upon mass and causing heavier gas moleculescontaining uranium-238 to move toward the outside of the cylinder andthe lighter gas molecules rich in uranium-235 to collect closer to thecenter. Gas centrifugation requires much less energy to achieve similarseparation to older gaseous diffusion processes, and thus gascentrifugation has largely replaced gaseous diffusion as an enrichmentmethod. The Zippe centrifuge is an enhancement on the standard gascentrifuge, the primary difference being the use of heat. The bottom ofthe rotating cylinder is heated, producing convection currents that movethe uranium-235 up the cylinder, where it can be collected.

A feature common to all large-scale enrichment schemes is that theyemploy a number of identical stages to produce successively higherconcentrations of uranium-235. Each stage concentrates the product ofthe previous step further before being sent to the next stage.Similarly, the tailings from each stage are returned to the previousstage for further processing. This sequential enriching system is calleda cascade. For example, gas centrifugation is performed with multiplecentrifugal runs using cascades of centrifuges.

Another expensive gas separation, for example, is separation ofundesired components from methane obtained downhole. Removal of carbondioxide and other components from the methane to provide apipeline-grade methane generally involves the use of very lowtemperatures and/or amine units. Such units can be costly and theiroperation time-consuming.

Accordingly, in view of the art, there is a need for efficient andeconomical apparatus and methods of separating gases. Desirably, theseparation is performed in the absence of a large cascade of separationstages and/or in the absence of cooling.

SUMMARY

Herein disclosed is an apparatus comprising (1) a porous rotorsymmetrically positioned about an axis of rotation and surrounding aninterior space; (2) an outer casing, wherein the outer casing and therotor are separated by an annular space; (3) a motor configured forrotating the rotor about the axis of rotation; (4) a feed inletpositioned along the axis of rotation and fluidly connected with theinterior space; and (5) a first outlet, wherein the first outlet isfluidly connected with the interior space. In embodiments, the feedinlet of the apparatus extends into the interior space.

A method of separating a feed gas into a first fraction and a secondfraction, the method including: introducing the feed gas into aninterior space within a rotor of a gas centrifuge, wherein the rotor ispermeable to gas and positioned about an axis of rotation; rotating therotor about the axis of rotation, whereby the heavy molecules of thefeed gas are forced toward the rotor; and extracting at least some ofthe first fraction from within the interior space through a sinteredmetal tube, and also extracting at least some of the second fractionfrom within the interior space, wherein the first fraction has anaverage molecular weight lower than the average molecular weight of thesecond fraction.

In embodiments, extracting the second fraction from the interior spacecomprises passing the second fraction through the rotor.

In embodiments, the method includes assisting extraction of the firstfraction via application of vacuum.

In embodiments, rotating the rotor about the axis of rotation provides arotational frequency of at least 7,500 RPM.

In embodiments, the sintered metal tube has an average pore sizeexclusive of particles above a cutpoint size.

In embodiments, the rotor includes a porous rotor, and the porous rotoris positioned symmetrically about the axis of rotation.

In aspects, the method may include extracting at least some of he secondfraction from within the interior space. In other aspects, extractingthe portion of the second fraction from the interior space may includepassing the portion of the second fraction through the porous rotor, andwherein extracting at least a portion of the first fraction from withinthe interior space extracting the portion through a sintered metal tube.

In embodiments, the rotor of the apparatus is substantially tubular. Inembodiments, the porous rotor of the apparatus is made from or comprisesa selectively-permeable material. In certain embodiments,selectively-permeable material comprises sintered metal or ceramic. Insome embodiments, the porous rotor of the apparatus has a diameter inthe range of from about 4 to about 12 inches. In some embodiments, theporous rotor of the apparatus has a length in the range of from about 8to about 20 inches. In certain embodiments, the motor of the apparatusis capable of providing a rotational frequency of the porous rotor of upto at least about 7,500 RPM. In certain embodiments, the apparatusfurther comprises a second outlet, wherein the second outlet is fluidlyconnected with the annular space.

Another aspect of the present disclosure includes a system comprising atleast one apparatus as described. In certain embodiments, the disclosedsystem further comprises at least one pump. In some embodiments, thesystem further comprises a feed inlet line in fluid communication withthe feed inlet and a first outlet line fluidly connected with the firstoutlet, wherein the at least one pump is positioned on the feed inletline or the first outlet line

Herein disclosed is also a method of separating a feed gas into a firstfraction and a second fraction, wherein the first fraction has anaverage molecular weight lower than the average molecular weight of thesecond fraction. The disclosed method comprises: (1) introducing thefeed gas into an interior space within a rotor of a gas centrifuge,wherein the rotor is permeable to gas and symmetrically positioned aboutan axis of rotation; (2) rotating the rotor about the axis of rotation,whereby the heavy molecules of the feed gas are forced toward the rotor;and (3) extracting the first fraction from within the interior spaceproximal the axis of rotation, leaving the second fraction therein. Insome embodiments, rotating the rotor about the axis of rotation providesa rotational frequency of at least 7,500 RPM.

In some embodiments, the method further comprises extracting the secondfraction from the interior space. In some cases, extracting the secondfraction from the interior space comprises passing the second fractionthrough the porous rotor and extracting the second fraction from theoutside of the rotor. In certain embodiments, extracting the secondfraction from the outside of the rotor further comprises assistingextraction of the first fraction via application of vacuum.

In certain embodiments, the porous rotor comprises sintered metal orceramic. In some embodiments, extracting the first fraction from withinthe interior space proximal the axis of rotation comprises extractingthe first fraction through a sintered metal tube. In certainembodiments, the sintered metal tube has an average pore size exclusiveof particles above a cutpoint size. In certain other embodiments,extracting the first fraction through a sintered metal tube furthercomprises assisting extraction of the first fraction via application ofvacuum to the interior space.

These and other embodiments and potential advantages will be apparent inthe following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the preferred embodiment of thepresent invention, reference will now be made to the accompanyingdrawing, wherein:

FIG. 1 is a schematic of a system according to an embodiment of thisdisclosure.

NOTATION AND NOMENCLATURE

As used herein, the use of the modifiers “light,” and “heavy” whenreferring to components or fractions of a gas stream indicate relativeweights, i.e. that the “light” component or fraction has a lowermolecular weight than the “heavy” component or fraction.

As used herein, the use of the modifiers “large” and “small” whenreferring to components or fractions of a gas stream indicate relativemolecular sizes, i.e. that the “large” component or fraction has agreater molecular size than the “small” component or fraction.

DETAILED DESCRIPTION

I. Overview.

Herein disclosed are a system and method of separating a feed gas into alight weight fraction or component and a heavy weight fraction orcomponent. The heavy weight fraction or component has a higher molecularweight than the light weight fraction or component.

Centrifugation relies on the effect of simulating gravity (usingreactive centrifugal acceleration) to separate molecules according totheir mass, and can be applied to both liquid and gaseous materials.Forces are applied by placing material inside a mechanism (i.e., acentrifuge) that rotates the material at high speed. The conventionalgas centrifuge relies on the principles of reactive centrifugal forceaccelerating molecules based upon mass. As conventionally performed in acascade of gas centrifuges in series and/or parallel, centrifugationyields separations of components having different molecular weights.According to this disclosure, centrifugation utilizing a sinteredmaterial (i.e., a porous rotor and/or a stationary sintered metal tube)allows effective separation by one or a few units, rather than requiringa cascade comprising a large number (up to thousands) of gascentrifuges.

The system and process are similar in theory to reverse osmosis, inwhich pressure is used to force a solution through a membrane, retainingthe solute on one side and allowing the pure solvent to pass to theother side.

II. System for Gas Separation.

The gas separation system of this disclosure comprises at least one gascentrifuge. The at least one gas centrifuge comprises at least oneporous sintered metal rotor or tube. In embodiments, the systemcomprises at least one porous rotor. The system may further comprise oneor more pumps. The gas separation system may further comprise one ormore flow control valves. The system may be in electronic communicationwith a control system for monitoring and controlling flow into and outof the gas centrifuge.

A system for gas separation according to this disclosure will now bedescribed with reference to FIG. 1. FIG. 1 is a schematic of a gasseparation system 100 according to an embodiment of this disclosure. Gasseparation system 100 comprises gas centrifuge 110, feed pump 130A,first outlet pump 130B, and second outlet pump 130C.

A system of this disclosure comprises at least one gas centrifuge 110.Each of the one or more gas centrifuges of the disclosed systemcomprises an outer casing, at least one porous component selected from aporous rotor or a porous outlet tube, at least one feed inlet, and atleast two product outlets. In the embodiment of FIG. 1, gas centrifuge110 comprises outer casing 165, porous rotor 185, feed inlet 120, firstfraction outlet 140, and second product outlet 190.

Gas centrifuge 110 comprises outer casing 165. As indicated in FIG. 1,outer casing 165 surrounds rotor 185. Outer casing 165 may becylindrical on its outer and/or inner surfaces. Outer casing 165 can bemade out of specific materials to prevent harmful materials from hurtingusers of gas centrifuge 110. In applications, components of gascentrifuge 110, such as casing 165, are made of stainless steel.

Porous Rotor or Stationary Porous Tube.

Each of the one or more gas centrifuges comprises at least one porouscomponent. The porous component may be a porous rotor or a stationaryporous tube. In embodiments, the gas separation system comprises aporous rotor. As indicated in the embodiment of FIG. 1, porous rotor 185is symmetrically positioned within casing 165 about an axis of rotation103. Porous rotor 185 is positioned within outer casing 165 such that aclearance or annular space 105 is created between outer wall 186 ofporous rotor 185 and the inner surface of outer casing 165. Rotor 185surrounds an interior space 122 configured such that the interior space122 may be evacuated of air prior to use to provide near frictionlessrotation when operating. Porous rotor 185 may comprise a selectivelypermeable or size-exclusion rotor. The rotor may be tubular in shape,e.g. a sintered metal tube. Porous rotor 185 is designed such that it ispermeable to gaseous components of a desired size.

In applications, the system comprises a porous tube. For example, inembodiments, first outlet 140 is one end of a stationary porous tube150. The walls of stationary porous tube 150 may comprise or containtherein size-exclusion or selectively-permeable material.

The porous component may comprise or contain sintered metal. Inembodiments, a porous rotor is made of or contains a selectivelypermeable cylinder made of any material which can be tailored for thedesired pore size and porosity and have the integral strength towithstand the rotation. Suitable porous material may be, for example,ceramic or stainless steel. In embodiments, the porous materialcomprises 316 stainless steel. In applications, the porosity (density)and average pore size of the porous material is tailored to allowpassage of components less than a desired cutpoint size while excludingpassage of components having a size greater than the cutpoint size.

The porous material may be sintered metal. In embodiments, the densityof the sintered metal is in the range of from about 3 g/cm³ to about 6g/cm³. In applications, the density of the sintered metal is greaterthan about 3 g/cm³, 3.5 g/cm³, 4 g/cm³, 4.5 g/cm³, 5 g/cm³, or 6 g/cm³.In applications, the density of the porous material is about 3.5 g/cm³,4 g/cm³, 4.5 g/cm³, 5 g/cm³, or 5.5 g/cm³. In embodiments, the averagepore size of a selectively permeable porous material is less than about200 μm, less than about 50 μm, less than about 20 μm, less than about 10μm, less than about 5 μm, less than about 3 μm, less than about 1 μm, orless than about 0.5 μm. In embodiments, the average pore size is in therange of Angstroms.

In embodiments, the porous material is formed by placing metal powder,e.g. stainless steel powder, in a mold and pressing it under highpressure. In embodiments, pressures of greater than 20,000 psig areutilized to compress the powder and form the porous material. Inembodiments, pressures of greater than 50,000 psig are utilized tocompress the powder and form the porous material. In embodiments,pressures of up to 150,000 psig are utilized to compress the powder andform the porous material. Pressing may reduce the thickness of astarting powder by at least 60%. The pressed material may then becalcined in an oven. To avoid shrinkage during formation, the materialmay be brought to a temperature approaching, but less than, the melttemperature, and cool down may be controlled over a sufficient durationto avoid/minimize shrinkage. Control of temperature during formation ofthe porous material of the rotor may also hinder the formation ofoxides.

The porous material of the rotor may be custom-tailored to provide gasflow paths of a desired tortuousity, porosity (density) and average poresize of the material. For example, a powder may be pressed into ahoneycomb structure or wax added and subsequently calcined to remove thehoneycomb or wax structure and leave honeycomb- or other patternedtailored paths or voids within the porous material of the rotor. In thismanner, the porous rotor may be designed with a desired average poresize and/or flow path.

The porous rotor may have a diameter and length determined to besuitable for a certain application, and the gas centrifuge may have anydesired nominal size. As such, the dimensions provided are not meant tobe limiting. In applications, porous rotor 185 has a diameter in therange of from about 2 inches to about 12 inches, from about 4 inches toabout 10 inches, from about 4 inches to about 8 inches, or from about 4inches to about 6 inches. Porous rotor 185 may have a vertical length inthe range of from about 8 inches to about 20 inches, from about 10inches to about 17 inches, or from about 12 inches to about 15 inches.The nominal capacity of gas centrifuge 110 may be about 10 gallons,about 5 gallons, or about 1 gallon. The thickness of the sinteredmaterial of the rotor may be tailored to provide a desired surface area.In embodiments, rotor 185 comprises sintered material having a thicknessof about ¼-inch, about ½-inch, about ¾-inch, or about 1-inch.

A desired permeability or average pore size of the porous component(e.g., a stationary metal outlet tube 150) may be obtained by providinga sintered material of a certain pore size (e.g., 30 to 100 μm) andsubsequently treating the sintered material with molecular sieve ormembrane. The external surfaces of the sintered metal material may becovered with one or more layers of molecular sieve. Suitable molecularsieves include, without limitation, carbon sieves, ALPOS, SAPOS,silicas, titanium silicates, and zeolites. In embodiments, the molecularsieve has a pore size in the range of from 3 angstrom (Å) to about 20 Å(about 0.3 nm to about 2 nm). The coating may be applied via methodssimilar to methods utilized to prepare catalyst surfaces on monolithand/or honeycomb catalytic converters that are used on automobilemufflers.

Porous rotor 185 may comprise or contain sintered metal. The rotor maybe made of or may contain a permeable material. The permeable materialmay be tailored for a desired pore size and porosity having integralstrength to withstand a desired operational rotation. In applications,the rotor comprises carbon fiber.

As mentioned hereinabove, rotor 185 may be porous and may comprise orcontain sintered metal. The rotor may be made of or may contain apermeable material. The permeable material may be tailored for a desiredpore size and porosity having integral strength to withstand a desiredoperational rotation. In embodiments, a porous rotor 185 comprises apermeable material 187 is sandwiched between an outer support 186 and aninner support 188. For example outer wall 186 and inner wall 188 ofporous rotor 185 may be a support material. By positioning the porousmaterial of rotor 185 between supports, increased strength may beprovided thereto. Inner and outer supports 186 and 188 may resemble abasket of support material in which the porous material is sandwiched.The inner and outer supports may be configured as a mesh basket (e.g., astainless steel mesh basket) in which the porous material is sandwiched.The inner and outer supports may be any material known to providesupport and through which gas may readily pass. Top 189 and bottom 184of rotor 185 may be impermeable to gas, or may comprise porous material.

The at least one gas centrifuge of the disclosed system furthercomprises at least one feed inlet. System 100 of the embodiment of FIG.1 comprises feed inlet 120. Feed inlet 120 is configured to introducefeed gas into the interior space 122 defined by porous rotor 185. Oneend 125 of feed inlet 120 is in fluid communication with interior space122 of gas centrifuge 110. Outlet end 125 of feed inlet 120 ispositioned proximal to axis of rotation 103. Outlet end 125 of feedinlet 120 is positioned between top 189 and bottom 184 of interior space122. In embodiments, outlet end 125 of feed inlet 120 is positionedwithin a lower portion of interior space 122. In embodiments, outlet end125 of feed inlet 120 is positioned at or near bottom 184 of interiorspace 122. In applications, outlet end 125 of feed inlet 120 ispositioned within the upper portion of interior space 122. Inembodiments, outlet end 125 of feed inlet 120 is positioned at or neartop 189 of interior space 122. The other end of feed inlet 120 isconfigured for introduction of reactant feed gas therein. Feed gas line115 is fluidly connected with the end of feed inlet 120 outside ofinterior space 122.

Each of the one or more gas centrifuges of the disclosed system furthercomprises at least two outlets configured for removing a light fractionand a heavy fraction respectively from the gas centrifuge. In theembodiment of FIG. 1, system 100 comprises light fraction or firstoutlet 140 and heavy fraction or second outlet 190.

Light fraction outlet 140 is in fluid communication with interior space122. In embodiments, light fraction outlet 140 is one end of a poroustube 150. The porous tube may be stationary or rotating during operationof system 100. The walls of porous tube 150 extend the entire length ofinterior space 122. In applications, the walls of porous tube 150comprise size-exclusion material as described hereinabove with respectto the porous component. In this manner, for example, the walls ofporous tube 150 may be selectively-permeable to gas of a desired size.In embodiments, therefore, first outlet 140 comprises one end of astationary sintered metal tube extending the entire length of porousrotor 185 along axis 103. The stationary sintered metal tube may beselectively-permeable to gas molecules having a size below a cutpointsize. For example, the walls of porous tube 150 may be permeable tomethane gas and impermeable to carbon dioxide. First or light fractionoutlet 140 is in fluid communication with light gas outlet line 155.

The inner surface of casing 165 and the outer surface 186 of porousrotor 185 create an annular region 105 therebetween. One end 192 ofheavy fraction outlet 190 is in fluid communication with annular region105. End 192 of product outlet 190 may be vertically positioned anywherewithin annular region 105, for example, towards the top, bottom, orcenter of annular region 105. In embodiments, end 192 of second outlet190 is positioned towards the bottom of annular region 105. Inembodiments, end 192 of product outlet 190 is positioned proximal theinner surface of casing 165. Alternatively, end 192 of product outlet190 is positioned distal the inner surface of casing 165. Alternatively,end 192 of product outlet 190 is horizontally positioned substantiallyhalfway between the inner surface of casing 165 and outer surface 186 ofrotor 185. Heavy fraction outlet 190 is in fluid communication withheavy fraction outlet line 195.

In embodiments, inlet and/or outlet ends of feed inlet 120, firstfraction outlet 140, and/or heavy fraction outlet 190 have a diameter of½ inch, ¾ inch, or 1-inch.

The gas centrifuge further comprises a motor coupled to the porousrotor. The motor is capable of providing rotation of the porous rotorabout an axis of rotation. Rotation of the rotor applies reactivecentrifugal force to the feed gas within the rotor. In the embodiment ofFIG. 1, for example, motor 145 is coupled to porous rotor 185 and iscapable of rotating porous rotor 185 about axis of rotation 103. Motor145 may be coupled to porous rotor 185 such that porous rotor 185 isrotatable in a clockwise direction or in a counter-clockwise direction.The high speed motor may be capable of rotational frequencies of up to90,000 RPM. Alternatively, some other means may provide the highrotational frequency. In embodiments, the high speed motor is capable ofproducing rotational frequencies of at least 5-, 7-, 7.5-, 10-, 15-,20-, 25-, 30-, 40-, 50-, 60-, 70-, 80-, or 90-thousand revolutions perminute (RPM).

The gas separation system may further comprise one or more flow controlvalves and/or pumps to control flow thereto and therefrom. One or morepumps may be operable to provide vacuum and/or pressure assist toenhance flow through gas centrifuge 110. For example, in the embodimentof FIG. 1 gas separation system 100 comprises three pumps, 130A, 130B,and 130C. Feed pump 130A is positioned on feed inlet line 115 and mayserve to force feed gas into gas centrifuge 110 under pressure. Firstoutlet pump 130B is positioned on product outlet line 155 and isoperable to control (assist or minimize) flow of gas via first outlet140. For example, first outlet pump 130B may serve to provide vacuumremoval of a light gas fraction from interior space 122. Second outletpump 130C is positioned on second outlet line 195 and is operable tocontrol (assist or minimize) flow of gas via second outlet 190.Alternatively or additionally, one or more flow control valves may bepositioned on feed line 115, first outlet line 155, and second outletline 195 respectively, and may be used to control flow therethrough.

System 100 may be in electronic communication with a control system,including a computer and sensors whereby flow of gas into and out offeed inlet 120, first outlet 140, and/or second outlet 190 and/orcomposition of gas within interior space 122 may be monitored and/orcontrolled.

Heaters.

It is envisaged that, for certain applications, all or portions of gascentrifuge 110 may be heated to enhance separation of gaseouscomponents. For example, all or portions of outer casing 165 may beheated using apparatus and methods as known in the art. In suchapplications, second outlet 190 may be desirably positioned within alower portion of annular space 105 and outlet end 125 of feed inlet 120may be positioned at or near bottom 184 of interior space 122, and/or anoutlet end of first outlet 140 may be positioned at or near top 189 ofinterior space 122.

Two or more gas centrifuges may be configured in series and/or parallel.In embodiments, a first outlet line 155 of a first gas centrifuge isfluidly connected with a feed gas line 115 of a second gas centrifuge.The first gas centrifuge is operable to produce a light gas fractioncomprising gas molecules below a first cutpoint size and a second gascentrifuge is operable to produce a second light gas fraction comprisinggas components below a second cutpoint size which is less than the firstcutpoint size. In embodiments, a second outlet line 195 of a first gascentrifuge is fluidly connected with a feed inlet line 115 of a secondgas centrifuge. In this embodiment, the first gas centrifuge is operableto produce a heavy gas fraction comprising gas molecules above a firstcutpoint size and a second gas centrifuge is operable to produce asecond heavy gas fraction comprising gas components above a secondcutpoint size which is less than the first cutpoint size. In thismanner, a feed gas may be fractionated into three or more gas fractionshaving different average molecular weights.

Outer casing 165 provides an enclosed vessel. Thus, the temperature andpressure within gas centrifuge 110 is adjustable as desired withindesign limitations. Without limitation, gas centrifuge 110 may beoperable at pressures up to at least 15 psig, 500 psig, 1000 psig, or1455 psig. Gas centrifuge 110 may be operable, without limitation, totemperatures up to 150° C., 200° C., 250° C., 300° C., 400° C., 450° C.,500° C., 550° C., or up to about 600° C.

III. Method of Gas Separation.

A method of separating light and heavy fractions of a gas according tothis disclosure will now be made with reference to FIG. 1. A gaseousfeed is introduced via feed line 115 and feed inlet 120 into gascentrifuge 110. The feed gas is introduced via inlet 120 into interiorspace 122 contained within the walls of rotor 185. In embodiments, thefeed gas is introduced at or near the top of interior space 122. Inembodiments, the feed gas is introduced at or near the bottom ofinterior space 122. The feed gas is introduced into interior region 122proximal axis of rotation 103.

The feed gas is subjected to reactive centrifugal force by motor 145,which causes rotation of rotor 185 about axis of rotation 103. The rotormay be rotated at a rotational frequency of up to 5-, 7-, 7.5-, 10-,15-, 20-, 25-, 30-, 40-, 50-, 60-, 70-, 80-, or 90-thousand RPM.Reactive centrifugal force pushes heavy molecular weight components ofthe gas feed toward inner walls 188 of rotor 185, while lower molecularweight components of the feed gas tend toward the center of interiorspace 122, toward axis of rotation 103. Low molecular weight gas isextracted via first outlet 140 and first outlet line 155. High molecularweight gas is extracted via second outlet 190 and second outlet line195. Vacuum and/or pressure assist may be provided by first pump 130Band/or second pump 130C to enhance extraction of light gas fraction viafirst outlet 140 and first outlet line 155 and/or heavy gas fraction viasecond outlet 190 and second gas outlet line 195. In applications, feedgas is introduced and light gas extracted while the composition of gaswithin interior space 122 is monitored or calculated based upon thecomposition of light gas extracted. Once the composition with interiorspace 122 reaches a desired concentration of heavy gas fraction, heavygas may be extracted via second outlet 190 and second gas outlet line195.

As discussed hereinabove, in applications, first outlet 140 is one endof or is in fluid communication with a porous sintered metal tube 150.Porous tube 150 may be made from a selectively-permeable through whichonly molecules below a desired cutpoint size may pass. In embodiments,feed gas is introduced into interior space 122 and vacuum is provided byfirst outlet pump 130B to assist in extraction of lower molecular weightgas components via outlet tube 140. Pressure may be applied to annularregion 105 via second outlet pump 130C or a suitable valve closed toprevent removal of gas through annular region 105. Light gas iswithdrawn from first outlet 140. When the concentration of heavy gascomponents in interior space 122 exceeds a desired value, introductionof feed is discontinued, extraction of low molecular weight gascompleted, and pump 130C operated and/or a suitable valve opened toprovide extraction of heavy gas components through porous rotor 185 andout via annular region 105.

Thus, vacuum and/or pressure assist may be used according to thedisclosed method, to extract desired components from gas centrifuge 110.

As gas centrifuge 110 is a closed vessel, surrounded by outer casing165, the operating temperature and pressure may be selected based ondesired performance. In applications, the operating temperature may bein the range of from about 25° C. to about 600° C. In applications, theoperating temperature is in the range of from about 100° C. or 150° C.to about 300° C., 400° C., or 500° C. In embodiments, gasseparation/fractionation is performed at room temperature. Inembodiments, gas separation/fractionation is performed at a temperaturewithin the range of 5° C. to 45° C. In embodiments, gasseparation/fractionation is performed at a temperature within the rangeof 20° C. to 40° C. In embodiments, gas separation/fractionation isperformed at a temperature within the range of 25° C. to 35° C. Theoperational pressure may be a desired pressure within the limits of thedesign materials. Utilization of high temperatures may allow gas phaseseparation of feeds which are not gaseous at room temperature.

The gas centrifugation process utilizes a design that provides for gasto constantly flow in and out of the gas centrifuge in certainapplications. Unlike most centrifuges which rely on batch processing,the disclosed gas centrifuge permits continuous or semi-continuousprocessing. In such applications, gas may be continuously orsemi-continuously extracted from interior space 122 and/or annularregion 105 via first outlet line 155 and second outlet line 195respectively.

Serial Operation.

In embodiments of the gas separation method, product gas from a firstgas centrifuge is introduced directly into a second gas centrifuge asfeed gas thereto. A first gas centrifuge may be operated to remove afirst heavy component from a feed gas, a second gas centrifuge operatedto remove a second heavy component from the feed gas, etc. In thismanner, a feed gas may be fractionated into three or more components orfractions.

Alternate Design:

In an embodiment, a non-porous rotor is combined with a poroussize-exclusion tube 150. Centrifugation will cause high molecular weightmolecules to tend toward the inner walls 188 of the non-porous rotor185, and low molecular weight gas molecules to tend toward the center ofinterior space 122 coincident axis of rotation 103. Once a concentrationof heavy molecular weight gas within interior space 122 exceeds adesired level, introduction of feed may be discontinued and heavy gasmay be removed from interior space 122. The concentration of heavy gasin interior space 122 may be determined directly or by calculation ofthe difference between the inlet gas fed and the light gas removed viafirst outlet 140 and first gas outlet line 155. A second outlet may beprovided to extract heavy gas from within interior space 122. Such asecond outlet may extend into interior space 122 symmetrically aboutaxis of rotation 103 and, once within interior space 122, may extend toa position proximal inner wall 188 of rotor 185.

EXAMPLES Example 1

In a specific embodiment, the feed gas continuously introduced into thegas centrifuge comprises dirty methane gas containing carbon dioxide andother gaseous impurities having a molecular weight greater than that ofmethane. In such instances, methane may be removed from interior space122 via first outlet 140, while a heavy fraction comprising carbondioxide and other heavy components is removed from annular region 105. Asize-exclusion outlet tube 150 having walls having a pore size inclusiveof methane and exclusive of carbon dioxide and other large molecules maybe used to enhance the separation. Vacuum 130B may be used to assist inwithdrawal of methane from the center of interior space 122. Pressuremay be applied to annular space 105 to prevent removal of gas throughrotor 185 and annular region 105 until a desired concentration of largemolecular weight components, including carbon dioxide, remains withininterior space 122. At this time, introduction of feed gas may bediscontinued. Vacuum 130B may be continued for a time to remove finalamounts of low molecular components from interior space 122. Then,vacuum 130B may be discontinued, and pump 130C utilized to extract highmolecular weight material through porous rotor 185 and annular region105. The light weight fraction may be introduced into a subsequent gascentrifuge and a light component or fraction comprising methane may beseparated from a second heavy fraction comprising, for example,nitrogen.

In embodiments, this separation of carbon dioxide from methane gas isperformed at ambient temperature. In embodiments, this separation ofcarbon dioxide from methane gas is performed at a temperature within therange of 5° C. to 45° C. In embodiments, the separation of carbondioxide from methane gas is performed at a temperature within the rangeof 20° C. to 40° C. In embodiments, the separation of carbon dioxidefrom methane gas is performed at a temperature within the range of 25°C. to 35° C. In this manner, pipeline-grade methane may be produced inthe absence of cooling and/or in the absence of amine systems.

Example 2

In an application, first outlet 140 is one end of or is fluidlyconnected with a porous tube 150 designed with a first cutpoint size.Gas component 1 has a molecular weight below the cutpoint size, whilegas components 2 and 3 have sizes above the cutpoint size. In thisembodiment, light gas fraction comprising gas component 1 may be removedfrom interior space 122 via first gas outlet 140. Heavy gas comprisingexcluded components 2 and 3 may be extracted from the gas centrifuge viasecond gas outlet 190. Heavy gas comprising excluded components 2 and 3may be subsequently introduced as feed gas into a second gas centrifugecomprising a first outlet 140 comprising a sintered metal tube designedwith a second cutpoint size greater than the first cutpoint size. Inthis manner, gas component 2 may be removed via first outlet 140 andthusly separated from gas component 3, which may be extracted throughporous rotor 185 and annular region 105. Vacuum and/or pressure assistmay be utilized to enhance separation.

Example 3

In a specific embodiment, the disclosed system and method are utilizedto enrich uranium. In such applications, the feed gas continuouslyintroduced into the size-exclusion gas centrifuge comprises gaseousuranium hexafluoride containing uranium-235 and uranium-238. In suchinstances, light gas component uranium-235 is removed via first outlet140 and heavy component uranium-238 is extracted via second outlet 190.

While preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Where numerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, and so forth). Use ofthe term “optionally” with respect to any element of a claim is intendedto mean that the subject element is required, or alternatively, is notrequired. Both alternatives are intended to be within the scope of theclaim. Use of broader terms such as comprises, includes, having, etc.should be understood to provide support for narrower terms such asconsisting of, consisting essentially of, comprised substantially of,and the like.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the preferred embodiments of the present invention.The disclosures of all patents, patent applications, and publicationscited herein are hereby incorporated by reference, to the extent theyprovide exemplary, procedural or other details supplementary to thoseset forth herein.

What is claimed is:
 1. A method of separating a feed gas into a firstfraction and a second fraction, the method comprising: introducing thefeed gas into a gas centrifuge, wherein the gas centrifuge comprises: arotor symmetrically positioned about an axis of rotation, wherein aninner wall of the rotor surrounds an interior space, a stationary outercasing enclosing the rotor, whereby an annular space is provided betweenan outer wall of the rotor and the stationary outer casing; a stationaryporous tube centered on the axis of rotation and extending the entirelength of the interior space, wherein the stationary porous tube isfluidly connected with a light gas outlet line at a top thereof; and afeed gas inlet cylinder extending through a top of and a distance intothe rotor, and surrounding a length of the stationary porous tube.rotating the rotor about the axis of rotation, whereby heavy moleculesof the feed gas are forced toward the inner wall of the rotor; andextracting at least a portion of the first fraction from the interiorspace through the stationary porous tube, and extracting at least aportion of the second fraction from the interior space, wherein thefirst fraction comprises one or more components of the feed gas having amolecular weight below a cutpoint size, and wherein the second fractioncomprises one or more components of the feed gas having a molecularweight above the cutpoint size.
 2. The method of claim 1, wherein therotor is permeable to gas, and wherein extracting the second fractionfrom the interior space further comprises passing the second fractionthrough the permeable rotor and thus into the annular space.
 3. Themethod of claim 1 further comprising assisting extraction of the firstfraction via application of vacuum via a pump positioned in the lightgas outlet line.
 4. The method of claim 3, wherein rotating the rotorabout the axis of rotation provides a rotational frequency of at least7,500 RPM.
 5. The method of claim 1, wherein the stationary porous tubehas an average pore size exclusive of particles above the cutpoint size,such that the first fraction can pass therethrough, while the secondfraction cannot.
 6. The method of claim 2, wherein the permeable rotorcomprises sintered metal.
 7. A method of separating a feed gas into afirst fraction and a second fraction, the method comprising: introducingthe feed gas into a gas centrifuge, wherein the gas centrifugecomprises: a rotor symmetrically positioned about an axis of rotation,wherein an inner wall of the rotor surrounds an interior space, astationary outer casing enclosing the rotor, whereby an annular space isprovided between an outer wall of the rotor and the stationary outercasing; a sintered metal tube centered on the axis of rotation andextending the entire length of the rotor, wherein the sintered metaltube is fluidly connected with a light gas outlet line at a top thereof;a feed gas inlet cylinder extending through a top of and a distance intothe rotor, and surrounding a length of the sintered metal tube; rotatingthe rotor about the axis of rotation, whereby heavy molecules of thefeed gas are forced toward the inner wall of the rotor; and extractingat least a portion of the first fraction from the interior space, andextracting at least a portion of the second fraction from the interiorspace; wherein the first fraction comprises one or more components ofthe feed gas having a molecular weight below a cutpoint size, andwherein the second fraction comprises one or more components of the feedgas having a molecular weight above the cutpoint size; and whereinextracting the at least a portion of the first fraction from theinterior space comprises extracting the at least a portion through thesintered metal tube and out the light gas outlet line.
 8. The method ofclaim 7, wherein the rotor is permeable to gas, and wherein extractingthe at least a portion of the second fraction from the interior spacefurther comprises passing the at least a portion of the second fractionthrough the permeable rotor and into the annular space, and extractingthe at least a portion of the second fraction from the annular space viaa heavy gas outlet extending through a lower portion of the outer casingand a horizontal distance into the annular space.
 9. The method of claim7, wherein the gas centrifuge further comprises a heavy gas outlet,wherein the heavy gas outlet enters the interior space proximal the axisof rotation, and extends horizontally to a position proximal the innerwall of the rotor, and wherein extracting the at least a portion of thesecond fraction from the interior space further comprises passing the atleast a portion of the second fraction through the heavy gas outlet. 10.The method of claim 7, wherein the first fraction comprises uranium-235,and wherein the second fraction comprises uranium-238.
 11. The method ofclaim 2 further comprising extracting the at least a portion of thesecond fraction from the annular space via a heavy gas outlet extendingthrough a lower portion of the outer casing and a horizontal distanceinto the annular space.
 12. The method of claim 11 further comprisingassisting extraction of the second fraction via a pump positioned in theheavy gas outlet.
 13. The method of claim 1, wherein the gas centrifugefurther comprises a heavy gas outlet, wherein the heavy gas outletenters the interior space proximal the axis of rotation, and extendshorizontally to a position proximal the inner wall of the rotor, andwherein extracting the at least a portion of the second fraction fromthe interior space further comprises passing the at least a portion ofthe second fraction through the heavy gas outlet.
 14. The method ofclaim 1 further comprising continuously introducing the feed gas intothe gas centrifuge via the feed gas inlet cylinder and extracting the atleast a first fraction from the gas centrifuge via the stationary poroustube and the light gas outlet line, while preventing removal of thesecond fraction; monitoring the composition of the gas within theinterior space; and, when the gas within the interior space attains adesired concentration of the second fraction, discontinuing extractionof the first fraction, and extracting the second fraction.
 15. Themethod of claim 14, wherein the rotor is permeable to gas, and whereinextracting the at least a portion of the second fraction from theinterior space further comprises passing the at least a portion of thesecond fraction through the permeable rotor and thus into the annularspace, and extracting the at least a portion of the second fraction fromthe annular space via a heavy gas outlet extending through a lowerportion of the outer casing and a horizontal distance into the annularspace.
 16. The method of claim 15 further comprising assistingextraction of the second fraction via a pump positioned on the heavy gasoutlet.
 17. The method of claim 14, wherein the gas centrifuge furthercomprises a heavy gas outlet, wherein the heavy gas outlet enters theinterior space proximal the axis of rotation, and extends horizontallyto a position proximal the inner wall of the rotor, and whereinextracting the at least a portion of the second fraction from theinterior space further comprises passing the at least a portion of thesecond fraction out the heavy gas outlet.
 18. The method of claim 1,wherein the first fraction comprises uranium-235, and wherein the secondfraction comprises uranium-238.